Bread – Egg YOLK replacement

There are two likely causes of soufflé problems.

1) Egg foam. Be sure that you're whipping them to peaks (soft peaks, as I recall) when you first whip them. Then, when adding the 2 mixtures together in 3rds, be sure that you're properly folding in the whites; this is a very specific technique, and easy to over-do.

2) Oven heat. Use an oven thermometer to check your oven's temp - it's probably wrong. Put some extra mass in that oven (like a baking stone or brick) to reduce wild temperature swings during baking.

But, as in the linked questions in the comments, all soufflés fall to some degree.

Cream has a high fat content, fat adds elasticity, flavor and a smooth mouth feel to ice cream. You can use 2% milk in ice cream instead of cream and it will work, however it will not have many of the desirable properties you get from cream. It will be harder and taste "weak" for lack of a better term.

If you want to make a lower fat ice cream then you can make up for the lack of milk fat somewhat by using more egg yolks and adding stabilizers like xanthan gum, guar gum, etc. See my answer to this question for a bit more detail on gums in ice cream.

It is possible to make a cream substitute by mixing 1/3 cup melted unsalted butter with 3/4 cup milk, but this would only work for recipes where the emulsion of fat in the liquid is not required - all you will get from this is milk with fat floating around in it. This may work in some baking applications, but it won't whip and it won't make ice cream you'd want to eat.